A parasitic microbe commonly found in cats might have helped shape entire human cultures by manipulating the personalities of infected individuals, according to a new study. Infection by a Toxoplasma gondii could make some individuals more prone to some forms of neuroticism and could lead to differences among cultures if enough people are infected, says Kevin Lafferty, a U.S. Geological Survey scientist at the University of California, Santa Barbara. In a survey of different countries, Lafferty found that people living in those with higher rates of T. gondii infection scored higher on average for neuroticism, defined as an emotional or...